Plasticizers are incorporated into resins to increase their flexibility, workability, and dispensability. Phthalates, especially, the high molecular weight phthalates (HMWP), are used as plasticizers in PVC. Alternatives to phthalates are desirable due to environmental, legislative and regulatory concerns. In particular, the uses of phthalates as plasticizers are under severe pressure. Hydrogenation of phthalates produces 1,2-cyclohexyl dicarboxylates, hereinafter also referred to as cyclohexanoates, which can also be used as plasticizers.
Previous research showed that catalysts consisting of Ru supported on alumina (Al2O3) with low surface areas are active for the hydrogenation of phthalate to cyclohexanoates. U.S. Pat. No. 5,936,126 (BASF) discloses the hydrogenation of phthalates to cyclohexyl dicarboxylates using catalysts consisting of Ru supported on low surface area alumina at 80 to 120° C. and under 10-20 MPa (100-200 atmospheres) pressure. US 2002/0019559 (BASF) discloses a catalyst for hydrogenation of phthalates comprising ruthenium deposited on an alumina support material that comprises macropores of greater than 50 nm in diameter.
It has also recently been discovered that materials consisting of Ru supported on a silica (SiO2) support with “remnant structure” produced by deposition of an organic ruthenium compound on a silica support to form an organic ruthenium complex on or in the support, followed by decomposition of the complex, have much higher activities and stabilities in the phthalate hydrogenation than reported Ru/Al2O3 catalysts. WO 2004/046076, WO 2004/045767 and WO 2004/046078 (ExxonMobil) disclose catalysts of Ru on silica supports prepared with the remnant structures. US 2012/0296111 (BASF) discloses an eggshell catalyst for hydrogenating carbocyclic aromatic compounds, such as phthalates, comprising a noble metal, such as ruthenium, deposited on a silica support material in which at least 90% of the pores present have a pore diameter of 6 to 12 nm. The catalysts may be prepared by depositing ruthenium acetate on the silica support and then reducing.
Large pore extruded silica is a commercially available catalyst support. US 2010/0133148 (ExxonMobil) discloses a hydrodesulfurization catalyst comprising cobalt and molybdenum salts impregnated on large pore silica supports. The large pore support is prepared by steam-treating a silica support material. The catalyst is prepared by impregnating the silica support with a solution containing the metal ions, an organic additive, which is an alcohol or aminoalcohol, an organic acid and an inorganic acid. US 2012/0184430 (Samsung) discloses the synthesis of a metal oxide support material, such as mesoporous silica, that has surface hydroxyl groups, including hydroxyl groups within its pores, and the preparation of a carbon dioxide reforming catalyst comprising a metal deposited onto that support material. However, the use of large pore silica as an effective support for ruthenium in a phthalate hydrogenation catalyst has not previously been achieved.
It has been found that large pore silica supports can facilitate the mass transfer of large molecules of phthalate during catalytic reactions, which can be beneficial to the catalyst activity for phthalate hydrogenation to cyclohexanoates. However, in order to have large pores and high crush strength, the silica support is steam-treated at high temperature. During the high temperature steaming treatments, the improved extrudate crush strength and large porosity are accompanied by decreases of hydroxyl group concentration and surface area of the steamed silica support. As a consequence, known strong and large pore silica supports usually have low surface areas and low concentration of Si—OH hydroxyl groups due to high temperature steaming. Si—OH hydroxyl groups are required for complexion to noble metals, such as ruthenium. Therefore, commercially available large pore silica is not particularly suitable for use as ruthenium supports for phthalate hydrogenation catalysts.
There remains a need for metal oxide-supported noble metal catalysts which are highly active in phthalate hydrogenation. In particular, there remains a need for a metal oxide support that can both facilitate the mass transfer of large molecules of phthalate during catalytic reactions and which has a high concentration of Si—OH hydroxyl groups for complexion to noble metals, such as ruthenium.